| /* |
| * Copyright (c) 2004, Swedish Institute of Computer Science. |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * 3. Neither the name of the Institute nor the names of its contributors |
| * may be used to endorse or promote products derived from this software |
| * without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND |
| * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE |
| * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
| * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
| * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
| * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
| * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
| * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
| * SUCH DAMAGE. |
| * |
| * This file is part of the Contiki operating system. |
| * |
| * Author: Adam Dunkels <adam@sics.se> |
| * |
| * $Id: pt-sem.h,v 1.4 2005/02/28 09:02:41 adamdunkels Exp $ |
| */ |
| |
| /** |
| * \addtogroup pt |
| * @{ |
| */ |
| |
| /** |
| * \defgroup ptsem Protothread semaphores |
| * @{ |
| * |
| * This module implements counting semaphores on top of |
| * protothreads. Semaphores are a synchronization primitive that |
| * provide two operations: "wait" and "signal". The "wait" operation |
| * checks the semaphore counter and blocks the thread if the counter |
| * is zero. The "signal" operation increases the semaphore counter but |
| * does not block. If another thread has blocked waiting for the |
| * semaphore that is signalled, the blocked thread will become |
| * runnable again. |
| * |
| * Semaphores can be used to implement other, more structured, |
| * synchronization primitives such as monitors and message |
| * queues/bounded buffers (see below). |
| * |
| * The following example shows how the producer-consumer problem, also |
| * known as the bounded buffer problem, can be solved using |
| * protothreads and semaphores. Notes on the program follow after the |
| * example. |
| * |
| \code |
| #include "pt-sem.h" |
| |
| #define NUM_ITEMS 32 |
| #define BUFSIZE 8 |
| |
| static struct pt_sem mutex, full, empty; |
| |
| PT_THREAD(producer(struct pt *pt)) |
| { |
| static int produced; |
| |
| PT_BEGIN(pt); |
| |
| for(produced = 0; produced < NUM_ITEMS; ++produced) { |
| |
| PT_SEM_WAIT(pt, &full); |
| |
| PT_SEM_WAIT(pt, &mutex); |
| add_to_buffer(produce_item()); |
| PT_SEM_SIGNAL(pt, &mutex); |
| |
| PT_SEM_SIGNAL(pt, &empty); |
| } |
| |
| PT_END(pt); |
| } |
| |
| PT_THREAD(consumer(struct pt *pt)) |
| { |
| static int consumed; |
| |
| PT_BEGIN(pt); |
| |
| for(consumed = 0; consumed < NUM_ITEMS; ++consumed) { |
| |
| PT_SEM_WAIT(pt, &empty); |
| |
| PT_SEM_WAIT(pt, &mutex); |
| consume_item(get_from_buffer()); |
| PT_SEM_SIGNAL(pt, &mutex); |
| |
| PT_SEM_SIGNAL(pt, &full); |
| } |
| |
| PT_END(pt); |
| } |
| |
| PT_THREAD(driver_thread(struct pt *pt)) |
| { |
| static struct pt pt_producer, pt_consumer; |
| |
| PT_BEGIN(pt); |
| |
| PT_SEM_INIT(&empty, 0); |
| PT_SEM_INIT(&full, BUFSIZE); |
| PT_SEM_INIT(&mutex, 1); |
| |
| PT_INIT(&pt_producer); |
| PT_INIT(&pt_consumer); |
| |
| PT_WAIT_THREAD(pt, producer(&pt_producer) & |
| consumer(&pt_consumer)); |
| |
| PT_END(pt); |
| } |
| \endcode |
| * |
| * The program uses three protothreads: one protothread that |
| * implements the consumer, one thread that implements the producer, |
| * and one protothread that drives the two other protothreads. The |
| * program uses three semaphores: "full", "empty" and "mutex". The |
| * "mutex" semaphore is used to provide mutual exclusion for the |
| * buffer, the "empty" semaphore is used to block the consumer is the |
| * buffer is empty, and the "full" semaphore is used to block the |
| * producer is the buffer is full. |
| * |
| * The "driver_thread" holds two protothread state variables, |
| * "pt_producer" and "pt_consumer". It is important to note that both |
| * these variables are declared as <i>static</i>. If the static |
| * keyword is not used, both variables are stored on the stack. Since |
| * protothreads do not store the stack, these variables may be |
| * overwritten during a protothread wait operation. Similarly, both |
| * the "consumer" and "producer" protothreads declare their local |
| * variables as static, to avoid them being stored on the stack. |
| * |
| * |
| */ |
| |
| /** |
| * \file |
| * Counting semaphores implemented on protothreads |
| * \author |
| * Adam Dunkels <adam@sics.se> |
| * |
| */ |
| |
| #ifndef __PT_SEM_H__ |
| #define __PT_SEM_H__ |
| |
| #include "pt.h" |
| |
| struct pt_sem { |
| unsigned int count; |
| }; |
| |
| /** |
| * Initialize a semaphore |
| * |
| * This macro initializes a semaphore with a value for the |
| * counter. Internally, the semaphores use an "unsigned int" to |
| * represent the counter, and therefore the "count" argument should be |
| * within range of an unsigned int. |
| * |
| * \param s (struct pt_sem *) A pointer to the pt_sem struct |
| * representing the semaphore |
| * |
| * \param c (unsigned int) The initial count of the semaphore. |
| * \hideinitializer |
| */ |
| #define PT_SEM_INIT(s, c) (s)->count = c |
| |
| /** |
| * Wait for a semaphore |
| * |
| * This macro carries out the "wait" operation on the semaphore. The |
| * wait operation causes the protothread to block while the counter is |
| * zero. When the counter reaches a value larger than zero, the |
| * protothread will continue. |
| * |
| * \param pt (struct pt *) A pointer to the protothread (struct pt) in |
| * which the operation is executed. |
| * |
| * \param s (struct pt_sem *) A pointer to the pt_sem struct |
| * representing the semaphore |
| * |
| * \hideinitializer |
| */ |
| #define PT_SEM_WAIT(pt, s) \ |
| do { \ |
| PT_WAIT_UNTIL(pt, (s)->count > 0); \ |
| --(s)->count; \ |
| } while(0) |
| |
| /** |
| * Signal a semaphore |
| * |
| * This macro carries out the "signal" operation on the semaphore. The |
| * signal operation increments the counter inside the semaphore, which |
| * eventually will cause waiting protothreads to continue executing. |
| * |
| * \param pt (struct pt *) A pointer to the protothread (struct pt) in |
| * which the operation is executed. |
| * |
| * \param s (struct pt_sem *) A pointer to the pt_sem struct |
| * representing the semaphore |
| * |
| * \hideinitializer |
| */ |
| #define PT_SEM_SIGNAL(pt, s) ++(s)->count |
| |
| #endif /* __PT_SEM_H__ */ |
| |
| /** @} */ |
| /** @} */ |
| |